It is for the situation where there are very few activities and it is cheaper to leave them unsigned. With the low demand, the cost of delivery increases because the routes need to consolidate deliveries between more distant regions

Anyway, if what you would like to achieve is to unassign all the jobs in a route under certain condition (e.g., with very few activities), you can use an InsertionEndsListener or an IterationEndsListener to conduct a post-processing after each iteration, and meanwhile, you can use a soft route constraint to encourage job insertion into routes with very few activities.